U.S. patent application number 12/519118 was filed with the patent office on 2010-06-17 for separator for fuel cell and method of forming collector of the separator.
This patent application is currently assigned to TOYOTA SHATAI KABUSHIKI KAISHA. Invention is credited to Kazunari Moteki, Hideto Tanaka.
Application Number | 20100151359 12/519118 |
Document ID | / |
Family ID | 40428797 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100151359 |
Kind Code |
A1 |
Tanaka; Hideto ; et
al. |
June 17, 2010 |
SEPARATOR FOR FUEL CELL AND METHOD OF FORMING COLLECTOR OF THE
SEPARATOR
Abstract
A separator 10 includes a separator body 11 and a collector 12.
The separator body 11 prevents mixed flow of fuel gas and oxidizer
gas. The collector 12 is formed from a metal lath MR in which the
angle between the direction of formation of strand portions
(through-hole formation portions) for forming through holes in a
meshy, step-like arrangement and the direction of formation of bond
portions (connection portions) for connecting the strand portions
to one another is about 60 degrees. By virtue of this, the
thickness of the collector 12 can be increased through reduction in
pitch P. Thus, a good gas supply performance is ensured through
reduction in pressure loss of introduced gas, and water generated
in an MEA 30 can be well drained by capillary action which arises
in the through holes.
Inventors: |
Tanaka; Hideto;
(Okazaki-shi, JP) ; Moteki; Kazunari;
(Okazaki-shi, JP) |
Correspondence
Address: |
ROSSI, KIMMS & McDOWELL LLP.
20609 Gordon Park Square, Suite 150
Ashburn
VA
20147
US
|
Assignee: |
TOYOTA SHATAI KABUSHIKI
KAISHA
Kariya-shi, Aichi
JP
TOYOTA JIDOSHA KABUSHIKI KAISHA
Toyota-shi, Aichi
JP
|
Family ID: |
40428797 |
Appl. No.: |
12/519118 |
Filed: |
August 25, 2008 |
PCT Filed: |
August 25, 2008 |
PCT NO: |
PCT/JP2008/065615 |
371 Date: |
July 28, 2009 |
Current U.S.
Class: |
429/514 ;
29/623.1 |
Current CPC
Class: |
H01M 8/04156 20130101;
H01M 8/0228 20130101; H01M 8/0245 20130101; Y02E 60/50 20130101;
H01M 2008/1095 20130101; H01M 8/0232 20130101; H01M 8/0204
20130101; Y10T 29/49108 20150115 |
Class at
Publication: |
429/514 ;
29/623.1 |
International
Class: |
H01M 8/02 20060101
H01M008/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 7, 2007 |
JP |
2007-232232 |
Claims
1. A separator for a fuel cell for supplying externally introduced
fuel gas and oxidizer gas to respective electrode layers of an
electrode structure of the fuel cell, characterized by comprising:
a flat-sheet-like separator body preventing mixed flow of the fuel
gas and the oxidizer gas through separation of the fuel gas and the
oxidizer gas from each other, and a collector disposed between the
electrode structure and the separator body, diffusing the fuel gas
or the oxidizer gas separated by the separator body, supplying the
diffused fuel gas or oxidizer gas to the corresponding electrode
layer, and collecting electricity generated through electrode
reactions in the electrode structure, an angle between a direction
of formation of through-hole formation portions for forming through
holes in a meshy, step-like arrangement and a direction of
formation of connection portions for connecting the through-hole
formation portions to one another being less than 90 degrees.
2. A separator for a fuel cell according to claim 1, wherein the
angle between the direction of formation of through-hole formation
portions and the direction of formation of connection portions in
the collector is about 60 degrees or greater.
3. A separator for a fuel cell according to claim 1 or 2, wherein
the collector is formed from a metal lath having a large number of
small-diameter through holes which are formed in a meshy, step-like
arrangement by means of strand portions corresponding to the
through-hole formation portions and bond portions corresponding to
the connection portions.
4. A method of forming a collector of a separator for a fuel cell
according to claim 1, characterized by using: a forming apparatus
having a stationary die whose end portion for placing a sheet
material thereon has a wedge-shaped section having an angle of less
than 90 degrees, and a shearing die which is disposed in a
direction of feed of the sheet material with respect to the
stationary die and moves in a direction of thickness of the sheet
material and in a direction of width of the sheet material, whose
end portion coming in contact with the sheet material has a
wedge-shaped section having an angle of less than 90 degrees so as
to be compatible with the wedge-shaped section of the end portion
of the stationary die, and which shears the sheet material so as to
form through holes in the sheet material, and comprising: a first
step of feeding the sheet material by a predetermined working
length, moving the shearing die in one direction with respect to
the direction of width of the sheet material, and moving the
shearing die in the direction of thickness of the sheet material so
as to form the through holes, and a second step of, subsequent to
the first step, feeding the sheet material by the predetermined
working length, moving the shearing die in the other direction with
respect to the direction of width of the sheet material, and moving
the shearing die in the direction of thickness of the sheet
material so as to form the through holes.
5. A method of forming a collector of a separator for a fuel cell
according to claim 4, wherein the first step and the second step
are sequentially repeated.
6. A method of forming a collector of a separator for a fuel cell
according to claim 4, wherein the shearing die has a plurality of
shearing edges formed at predetermined intervals.
7. A method of forming a collector of a separator for a fuel cell
according to claim 6, wherein each of the shearing edges has a
trapezoid or triangular shape as viewed on a section taken
perpendicular to the direction of feed of the sheet material.
Description
TECHNICAL FIELD
[0001] The present invention relates to a separator for use in a
fuel cell, particularly, a polymer electrolyte fuel cell, and to a
method of forming a collector of the separator.
BACKGROUND ART
[0002] Generally, a polymer electrolyte fuel cell includes an
electrode structure which, in turn, includes an anode electrode
layer formed on one side of an electrolyte membrane and a cathode
electrode layer formed on the other side of the electrolyte
membrane. In the polymer electrolyte fuel cell, fuel gas (e.g.,
hydrogen gas) and oxidizer gas (e.g., air) are externally supplied
to the anode electrode layer and the cathode electrode layer,
respectively. The supply of fuel gas and oxidizer gas induces
electrode reactions in the electrode structure, thereby generating
electricity. Thus, in order to improve the electricity generation
efficiency of the polymer electrolyte fuel cell, it is important to
efficiently supply the electrode structure the fuel gas and
oxidizer gas required for electrode reactions.
[0003] Meanwhile, the polymer electrolyte fuel cell has a separator
for supplying the anode electrode layer and the cathode electrode
layer with the externally supplied fuel gas and oxidizer gas,
respectively, in a mutually separated condition. Conventionally,
the electricity generation efficiency of the polymer electrolyte
fuel cell has been improved through improvement of efficiency in
supply of fuel gas and oxidizer gas via the separator.
[0004] For example, Japanese Patent Application Laid-Open (kokai)
No. 2007-87768 discloses a separator for a fuel cell. The separator
includes a separator body which prevents mixed flow of fuel gas and
oxidizer gas through separation of the fuel gas and the oxidizer
gas from each other, and a collector which is formed from a lath
metal (metal lath) having a large number of through holes formed in
a meshy, step-like arrangement, forms a gas passageway for
supplying the fuel gas or the oxidizer gas to the corresponding
electrode layer, and collects generated electricity. In the fuel
cell which employs the thus-configured separator, the fuel gas or
the oxidizer gas separated by the separator body passes through the
meshy through holes formed in the collector, thereby being
sufficiently diffused. Therefore, the electricity generation
efficiency of the polymer electrolyte fuel cell can be
improved.
DISCLOSURE OF THE INVENTION
[0005] The collector disclosed in Japanese Patent Application
Laid-Open (kokai) No. 2007-87768 is formed from a metal lath
manufactured by a general manufacturing method. Thus, usually, the
thickness of the collector is small. As a result, resistance
associated with flow of fuel gas or oxidizer gas to the
corresponding electrode layer; i.e., pressure loss, may increase.
Therefore, sufficient supply of fuel gas and oxidizer gas to the
respective electrode layers may fail, leaving room for improvement.
In this connection, a conceivable practice to increase the
thickness of the collector; i.e., the thickness of metal lath, is,
for example, to increase working length in shearing a material
(e.g., metal sheet) in a staggered arrangement. However, since
deformation resistance of the material is low, the increase of
working length encounters difficulty in the manufacture of a metal
lath having an appropriate thickness. Use of a metal lath having an
inappropriate thickness may result in, for example, nonuniformity
in shape of formed through holes and an increase in pressure
loss.
[0006] Also, in the polymer electrolyte fuel cell, as electrode
reactions using the fuel gas and oxidizer gas proceed in the
electrode structure, water is generated in the anode electrode
layer or the cathode electrode layer according to the ion exchange
characteristic of the electrolyte membrane. The thus-generated
water, for example, covers the surface of the anode electrode layer
or the surface of the cathode electrode layer or adheres to the
through holes formed in the collector, potentially impairing good
supply of fuel gas or oxidizer gas. Thus, as the electrode
reactions proceed, the possibility of a drop in electricity
generation efficiency of the fuel cell increases. Also, in the case
where the polymer electrolyte fuel cell is installed in an
environment susceptible to low temperatures, the generated water
remaining therein may be frozen, causing a failure in sufficient
supply of fuel gas or oxidizer gas. As a result, the
low-temperature start-up performance of the fuel cell may
deteriorate. Therefore, water generated through electrode reactions
must be efficiently drained outward.
[0007] The present invention has been achieved for solving the
above-mentioned problems, and an object of the invention is to
provide a separator for a fuel cell which exhibits both good
performance of supply of fuel gas and oxidizer gas and good
performance of drainage of water generated through electrode
reactions.
[0008] To achieve the above object, according to a feature of the
present invention, a separator for a fuel cell for supplying
externally introduced fuel gas and oxidizer gas to respective
electrode layers of an electrode structure of the fuel cell
comprises a flat-sheet-like separator body preventing mixed flow of
the fuel gas and the oxidizer gas through separation of the fuel
gas and the oxidizer gas from each other, and a collector disposed
between the electrode structure and the separator body, diffusing
the fuel gas or the oxidizer gas separated by the separator body,
supplying the diffused fuel gas or oxidizer gas to the
corresponding electrode layer, and collecting electricity generated
through electrode reactions in the electrode structure, an angle
between a direction of formation of through-hole formation portions
for forming through holes in a meshy, step-like arrangement and a
direction of formation of connection portions for connecting the
through-hole formation portions to one another being less than 90
degrees.
[0009] In this case, the angle between the direction of formation
of through-hole formation portions and the direction of formation
of connection portions in the collector may be, for example, about
60 degrees or greater. Also, the collector may be formed from a
metal lath having a large number of small-diameter through holes
which are formed in a meshy, step-like arrangement by means of
strand portions corresponding to the through-hole formation
portions and bond portions corresponding to the connection
portions.
[0010] A method of forming a collector of a separator for a fuel
cell may use a forming apparatus having a stationary die whose end
portion for placing a sheet material thereon has a wedge-shaped
section having an angle of less than 90 degrees, and a shearing die
which is disposed in a direction of feed of the sheet material with
respect to the stationary die and moves in a direction of thickness
of the sheet material and in a direction of width of the sheet
material, whose end portion coming in contact with the sheet
material has a wedge-shaped section having an angle of less than 90
degrees so as to be compatible with the wedge-shaped section of the
end portion of the stationary die, and which shears the sheet
material so as to form through holes in the sheet material. The
method may comprise a first step of feeding the sheet material by a
predetermined working length, moving the shearing die in one
direction with respect to the direction of width of the sheet
material, and moving the shearing die in the direction of thickness
of the sheet material so as to form the through holes, and a second
step of, subsequent to the first step, feeding the sheet material
by the predetermined working length, moving the shearing die in the
other direction with respect to the direction of width of the sheet
material, and moving the shearing die in the direction of thickness
of the sheet material so as to form the through holes.
[0011] In this forming method, for example, the first step and the
second step may be sequentially repeated. Also, the shearing die
may have a plurality of shearing edges formed at predetermined
intervals. In this case, each of the shearing edges may have, for
example, a trapezoid or triangular shape as viewed on a section
taken perpendicular to the direction of feed of the sheet
material.
[0012] According to the above-mentioned configurations, the
collector which partially constitutes the separator for a fuel cell
can be formed from, for example, a metal lath and thus can have a
large number of through holes having a small diameter and formed in
a meshy, step-like arrangement. Thus, the collector causes the fuel
gas or the oxidizer gas separated by the separator body to pass
through a large number of the through holes formed therein, whereby
the gas can be supplied to the corresponding electrode layer in a
well diffused condition. Also, in the collector, the angle between
the direction of formation of the through-hole formation portions
(strand portions) and the direction of formation of the connection
portions (bond portions) can be less than 90 degrees; more
specifically, about 60 degrees to less than 90 degrees. Thus, when
the collector is disposed between the electrode structure and the
separator body, the plane of opening of each of the through holes
can have a large angle with respect to the electrode structure
(more specifically, the electrode layer) or the separator body;
i.e., the through holes are in a steep posture.
[0013] Thus, even in the case of formation of through holes having
the same diameter as that of conventional through holes, the
thickness of the collector can be increased to an extent
corresponding to the steepness. In other words, by means of forming
through holes under working conditions sufficiently good as to be
free from occurrence of the aforementioned defective working, the
thickness of the collector can be increased. By virtue of an
increase in thickness of the collector, pressure loss associated
with flow of gas can be lowered, thereby ensuring sufficient gas
supply performance with respect to supply of fuel gas and oxidizer
gas required for electrode reactions in the electrode structure.
Therefore, the electricity generation efficiency of the fuel cell
can be greatly improved.
[0014] By means of setting the angle between the direction of
formation of the through-hole formation portions and the direction
of formation of the connection portions to less than 90 degrees
(more specifically, about 60 degrees), the distance between the
connection portions in the collector can be reduced. In other
words, the through holes can be formed in proximity to one another.
In a state in which the through holes are in proximity to one
another, when water generated through electrode reactions reaches
the vicinity of the collector, the capillary action which arises in
the through holes renders the generated water more fluid. Also, in
a state in which a fuel gas or oxidizer gas flows; i.e., in a state
in which the fuel cell is activated, in addition to the capillary
action, pressure for flow of gas acts on the generated water. Thus,
the generated water, together with a portion of unreacted gas, can
be efficiently drained to the exterior of the fuel cell.
Accordingly, even in a state in which water is generated along with
progress of electrode reactions, the generated water can be well
drained. Therefore, good gas supply performance can be maintained,
whereby a drop in electricity generation efficiency of the fuel
cell can be prevented.
[0015] Furthermore, since the distance between the connection
portions in the collector can be reduced, contacts between the
electrode structure (more specifically, the electrode layer) or the
separator body and the connection portions of the collector can be
rendered dense. Thus, the collector can efficiently collect and
output electricity generated through electrode reactions. Also,
particularly, the dense contacts between the electrode structure
and the connection portions of the collector can greatly reduce
deformation of the electrode structure, whose substrate is a thin
polymer membrane. Thus, a mechanical load which stems from the
deformation and is imposed on the electrode structure can be
greatly reduced, thereby preventing deterioration of the electrode
structure which would otherwise result from the mechanical
load.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic view relating to an embodiment of the
present invention and partially showing a fuel cell stack which
employs separators for a fuel cell of the present invention;
[0017] FIG. 2 is a schematic, perspective view showing a separator
body of the separator of FIG. 1;
[0018] FIGS. 3(a) and 3(b) are schematic views for explaining a
collector (metal lath) of FIG. 1;
[0019] FIGS. 4(a) and 4(b) are schematic views for explaining the
configuration of a metal-lath-forming apparatus for manufacturing
the metal lath;
[0020] FIGS. 5(a) and 5(b) are schematic views for explaining the
configuration of a conventional metal-lath-forming apparatus for
manufacturing the metal lath;
[0021] FIGS. 6(a) and 6(b) are schematic views for explaining, as a
comparative example, a metal lath manufactured by the
metal-lath-forming apparatus of FIG. 5;
[0022] FIG. 7 is a view for explaining the difference in pitch
between the metal lath shown in FIG. 3 and the metal lath shown in
FIG. 6;
[0023] FIG. 8 is a schematic, perspective view for explaining a
state of assembly of frames and an MEA shown in FIG. 1; and
[0024] FIG. 9 is a pair of schematic views showing modified through
holes of the collector (metal lath).
BEST MODE FOR CARRYING OUT THE INVENTION
[0025] An embodiment of the present invention will next be
described in detail with reference to the drawings. FIG. 1 is a
sectional view schematically showing a portion of a polymer
electrolyte fuel cell stack which employs separators 10 for a fuel
cell (hereinafter, referred to merely as the separators 10)
according to the present embodiment. The fuel cell stack is a stack
of cells. A single cell includes two separators 10, two frames 20,
and an MEA 30 (Membrane-Electrode Assembly 30). The frames 20 and
the MEA 30 are disposed in layers between the separators 10.
[0026] When, for example, fuel gas such as hydrogen gas, and
oxidizer gas such as air are introduced to the cells from the
exterior of the fuel cell stack, electrode reactions occur in the
MEAs 30, thereby generating electricity. Hereinafter, fuel gas and
oxidizer gas may be collectively referred to merely as gas.
[0027] As shown in FIG. 1, each of the separators 10 includes a
separator body 11 for preventing a mixed flow of gas introduced
into the fuel cell stack, and a collector 12 for uniformly
diffusing externally supplied fuel gas or oxidizer gas to the MEA
30 and for collecting electricity generated through electrode
reactions.
[0028] The separator body 11 is formed from a metal sheet (e.g., a
stainless steel sheet having a thickness of about 0.1 mm). Another
material which can be used to form the separator body 11 is, for
example, a steel sheet which has undergone anticorrosive treatment
such as gold plating. In place of a metal sheet, an electrically
conductive nonmetal material (e.g., carbon) may also be used to
form the separator body 11. As shown in FIG. 2, the separator body
11 is formed into a substantially square, flat-sheet-like shape.
Two gas inlets 11a and two gas outlets 11b are formed in a
peripheral region of the separator body 11 in such a manner that
the gas inlets 11a face the corresponding gas outlets 11b. A pair
consisting of the gas inlet 11a and the gas outlet 11b is oriented
substantially orthogonal to the other pair consisting of the gas
inlet 11a and the gas outlet 11b.
[0029] Each of the gas inlets 11a assumes the form of an elongated
through hole and allows fuel gas or oxidizer gas supplied from the
exterior of the fuel cell stack to be introduced therethrough into
the corresponding cell and to flow therethrough so as to be
supplied to other stacked cells. Each of the gas outlets 11b also
assumes the form of an elongated through hole and allows discharge
therethrough, to the exterior of the fuel cell stack, of gas which
has been introduced into the corresponding cell but remains
unreacted in the MEA 30, as well as flow therethrough of unreacted
gas from other stacked cells.
[0030] As shown in FIG. 3(a), the collector 12 is formed from a
metal sheet having a large number of small-diameter through holes
formed in a meshy, step-like arrangement (hereinafter, this metal
sheet is called a metal lath MR). This metal lath MR is formed from
a sheet material (e.g., stainless steel sheet) having a thickness
of about 0.1 mm. The through holes formed in large quantity have a
hole diameter of about 0.1 mm to 1 mm. As shown in FIG. 3(b), which
is a side view as viewed from the left-right direction in FIG.
3(a), in the metal lath MR, those portions which form the through
holes (hereinafter, these portions are called strand portions) are
sequentially connected in an overlapping manner (hereinafter, these
connection portions are called bond portions). Herein, the strand
portions of the metal lath MR correspond to through-hole formation
portions of the collector 12, and the bond portions of the metal
lath MR correspond to connection portions of the collector 12. Next
will be described lath machining for forming the metal lath MR.
[0031] The metal lath MR is formed by use of a metal-lath-forming
apparatus R, which is schematically shown in FIG. 4(a), in such a
manner that a large number of through holes are formed in a
stainless steel sheet S in a meshy, step-like arrangement. The
metal-lath-forming apparatus R includes feed rollers OR for feeding
the stainless steel sheet S; a press mechanism OK for appropriately
fixing the stainless steel sheet S during working; and a blade
stamp H for sequentially shearing the stainless steel sheet S so as
to form through holes in a meshy arrangement. The stainless steel
sheet S may assume the form of a precut sheet having a
predetermined length or the form of a coil.
[0032] The blade stamp H consists of a lower blade SH which serves
as a stationary die and is fixed to an unillustrated base and on
which the stainless steel sheet S is placed, and an upper blade UH
which serves as a shearing die and can move in the direction of
thickness of the stainless steel sheet S (in the vertical direction
on the paper on which FIG. 4(a) appears) and in the direction of
width of the stainless steel sheet S (in the direction
perpendicular to the paper on which FIG. 4(a) appears). As shown in
FIG. 4(a), the lower blade SH is formed such that its end portion
coming in contact with the stainless steel sheet S has a
wedge-shaped section having an angle of, for example, about 60
degrees. As shown in FIG. 4(b), the edge of the lower blade SH
coming in contact with the stainless steel sheet S is formed
straight. The slope of the lower blade SH and the press mechanism
OK hold the stainless steel sheet S therebetween, thereby fixing
the stainless steel sheet S.
[0033] As shown in FIG. 4(a), the upper blade UH is formed such
that its end portion coming in contact with the stainless steel
sheet S has a wedge-shaped section having an angle of, for example,
about 60 degrees so as to be compatible with the wedge-shaped
section of the end portion of the lower blade SH. As shown in FIG.
4(b), in order to form cuts in the stainless steel sheet S by
shearing work and to form through holes by stretching work, the
cutting edge of the upper blade UH has a shape resembling a
plurality of trapezoids arranged at predetermined intervals. The
upper blade UH can be moved in the direction of thickness of the
stainless steel sheet S and in the direction of width of the
stainless steel sheet S by means of an unillustrated AC
servomechanism.
[0034] In the thus-configured metal-lath-forming apparatus R,
first, the feed rollers OR feed the stainless steel sheet S to the
blade stamp H by a predetermined working length. The press
mechanism OK and the slope of the lower blade SH fixedly hold the
stainless steel sheet S therebetween. When the feed rollers OR feed
the stainless steel sheet S to the blade stamp H, the upper blade
UH of the blade stamp H lowers toward the lower blade SH; i.e., in
the direction of thickness of the stainless steel sheet S, and
shears the stainless steel sheet S by means of the substantially
trapezoidal cutting edges and in cooperation with the lower blade
SH, thereby forming cuts in the stainless steel sheet S.
Subsequently, the upper blade UH lowers further to the bottom
position of its stroke, thereby bending and stretching portions of
the stainless steel sheet S which are in contact with the cutting
edges of the upper blade UH, and thus forming strand portions.
Then, the upper blade UH returns from the bottom position to the
upper origin position of its stroke. In this manner, the strand
portions to which the shape of the upper blade UH is transferred
are formed on the stainless steel sheet S.
[0035] Subsequently, the feed rollers OR again feed the stainless
steel sheet S to the blade stamp H by the predetermined working
length. At this time, the upper blade UH moves (i.e., is offset) in
the horizontal direction by half a working pitch; more
specifically, by a cutting-edge length WH of the upper blade UH.
Then, the upper blade UH lowers again as mentioned above. This
performs the above-mentioned cutting work and bending-stretching
work on the stainless steel sheet S at positions which are offset
leftward or rightward by half the working pitch from the strand
portions formed by the previous lowering stroke of the upper blade
UH, thereby forming new strand portions to which the shape of the
upper blade UH is transferred. Thus, as shown in FIG. 3(a),
substantially hexagonal through holes are formed in the stainless
steel sheet S by means of the strand portions.
[0036] Repeating the above-mentioned operations forms continuously
the metal lath MR in which a large number of through holes are
formed in a staggered meshy arrangement. Since the upper blade UH
has a plurality of substantially trapezoidal cutting edges,
lowering the upper blade UH leaves cut-free portions on the
stainless steel sheet S. The cut-free portions of the stainless
steel sheet S become bond portions of the metal lath MR, whereby
the strand portions are sequentially connected in an overlapping
manner. The metal lath MR is cut so as to have predetermined
dimensions, thereby forming the collector 12.
[0037] As mentioned previously, the end portion of the lower blade
SH and the end portion of the upper blade UH which come into
contact with the stainless steel sheet S have a wedge-shaped
section having an angle of about 60 degrees. The metal lath MR is
formed by means of the lower blade SH and the upper blade UH each
having the wedge-like shape. Thus, in the metal lath MR formed by
the metal-lath-forming apparatus R, as shown in FIG. 3(b), the
angle between the direction of formation of the simultaneously
formed bond portions (i.e., the bond portions in the same row) and
the direction of formation of the strand portions connected to the
bond portions and forming the through holes becomes less than 90
degrees; more specifically, about 60 degrees.
[0038] As schematically shown in FIGS. 5(a) and 5(b), a general
manufacturing method used to form a conventional metal lath SMR
uses a metal-lath-forming apparatus R' employing a lower blade SH'
and an upper blade UH' whose end portions coming into contact with
the stainless steel sheet S have a section having a flat end,
rather than a wedge-shaped section. Similar to the above-mentioned
manufacture of the metal lath MR, the metal-lath-forming apparatus
R' using the lower blade SH' and the upper blade UH' forms a large
number of through holes in the stainless steel sheet S in a
staggered meshy arrangement, thereby yielding the metal lath SMR.
In the conventional metal-lath-forming apparatus R' using the lower
blade SH' and the upper blade UH', the lower blade SH' and the
press mechanism OK hold the stainless steel sheet S therebetween in
such a manner that the stainless steel sheet S lies in the
horizontal direction, and the upper blade UH' moves up and down in
the direction of thickness of the stainless steel sheet S; i.e., in
the vertical direction. Accordingly, as shown in FIG. 6, in the
manufactured metal lath SMR, the angle between the direction of
formation of bond portions and the direction of formation of strand
portions becomes about 90 degrees.
[0039] By contrast, in manufacture of the metal lath MR, while the
lower blade SH and the press mechanism OK hold the stainless steel
sheet S therebetween in such a manner that the stainless steel
sheet S is inclined upward at about 60 degrees with respect to the
horizontal direction, the upper blade UH moves up and down in the
vertical direction. Thus, as shown in FIG. 3(b), the angle between
the direction of formation of bond portions and the direction of
formation of strand portions becomes about 60 degrees. That is,
when the metal lath MR and the metal lath SMR are placed on a
horizontal plane, as shown in FIG. 7, the angle between the
horizontal plane and a plane which contains the strand portions of
the metal lath MR is greater than that between the horizontal plane
and a plane which contains the strand portions of the metal lath
SMR. In other words, the through holes which are formed in the
metal lath MR in a meshy arrangement are in a so-called steeper
posture as compared with the through holes which are formed in the
conventional metal lath SMR in a meshy arrangement.
[0040] Since the metal lath MR can have a large angle between the
formed strand portions and the horizontal plane, the metal lath MR
can have a sufficient formed thickness. As will be described later,
in order to ensure good flow of fuel gas or oxidizer gas, a gap
between the separator body 11 and the MEA 30 must be increased. In
this case, since the collector 12 formed from the metal lath MR can
have a large thickness, the gap can be increased accordingly.
[0041] By contrast, in manufacture of the conventional metal lath
SMR, in order to increase the formed thickness of the metal lath
SMR, the working length of the stainless steel sheet S to be fed by
the feed rollers OR must be increased. However, if, in order to
impart a large formed thickness to the metal lath SMR, the working
length of the stainless steel sheet S to be fed by the feed rollers
OR is increased, difficulty is encountered in forming strand
portions, since deformation resistance of the thin stainless steel
sheet S is low.
[0042] Also, as shown in FIG. 7, in the metal lath MR, the distance
between the bond portions; i.e., a pitch P, can be reduced. Thus,
when the MEA 30 and the collector 12 formed from the metal lath MR
are assembled together in contact with each other, contact
intervals between the MEA 30 and the connection portions of the
collector 12 can be shortened (rendered dense). Accordingly, the
deformation (waviness) of the MEA 30 in an assembled condition can
be greatly reduced. Therefore, a mechanical load imposed on the MEA
30 can be greatly reduced; thus, sufficient durability of the MEA
30 can be ensured.
[0043] By contrast, as shown in FIG. 7, in the conventional metal
lath SMR, the distance between the bond portions; i.e., a pitch P',
is increased. Particularly, in the case where the working length is
increased in order to increase the formed thickness of the metal
lath SMR, the pitch P' is increased further. Thus, for example,
when the collector 12 is formed from the metal lath SMR, contact
intervals between the MEA 30 and the connection portions of the
collector 12 are lengthened. As a result, the MEA 30 in an
assembled condition is deformed (waved), and an associated
imposition of mechanical load on the MEA 30 may impair
durability.
[0044] As shown in FIG. 8, a frame 20 consists of two resin sheet
bodies 21 and 22 of the same structure. One side of each of the
resin sheet bodies 21 and 22 is fixedly attached to a corresponding
one of two separators 10 (more specifically, two separator bodies
11). The resin sheet bodies 21 and 22 have outside dimensions
substantially identical with those of the separator body 11 and a
thickness slightly smaller than the formed height of the collector
12. The resin sheet bodies 21 and 22 are laminated together while
being disposed in such a manner as to differ in an angular, planar
orientation by about 90 degrees. Various resin materials can be
employed to form the resin sheet bodies 21 and 22. Preferably, a
glass epoxy resin is employed.
[0045] Through holes 21a and 21b which correspond to and are shaped
substantially similar to the gas inlet 11a and the gas outlet 11b,
respectively, are formed in a peripheral region of the resin sheet
body 21, and through holes 22a and 22b which correspond to and are
shaped substantially similar to the gas inlet 11a and the gas
outlet 11b, respectively, are formed in a peripheral region of the
resin sheet body 22. In a state in which a single cell is formed,
the through holes 21a, 21b, 22a, and 22b positionally coincide with
the corresponding gas inlets 11a and gas outlets 11b. Accommodation
holes 21c and 22c for accommodating the respective collectors 12
joined to the separator bodies 11 are formed in substantially
central regions of the resin sheet bodies 21 and 22, respectively.
In the form of a single cell, the accommodation hole 21c of the
resin sheet body 21 communicates with a pair consisting of the gas
inlet 11a and the gas outlet 11b of the separator body 11 fixed to
the resin sheet body 21, and communicates with the through holes
22a and 22b of the resin sheet body 22, whereas the accommodation
hole 22c of the resin sheet body 22 communicates with the other
pair consisting of the gas inlet 11a and the gas outlet 11b of the
separator body 11 fixed to the resin sheet body 22, and
communicates with the through holes 21a and 21b of the resin sheet
body 21.
[0046] As a result of formation of the accommodation holes 21c and
22c, the lower surface (upper surface) of the attached separator
body 11, the inner peripheral surface of the accommodation hole 21c
(22c), and the upper surface (lower surface) of the MEA 30 define a
space (hereinafter, called a gas flow space). For example, fuel gas
can be introduced into the corresponding gas flow space through one
gas inlet 11a, whereas oxidizer gas can be introduced into the
corresponding gas flow space through the other gas inlet 11a and
through the through hole 21a. Also, unreacted gas which has passed
through the gas flow space can be discharged outward through one
gas outlet 11b or through the other gas outlet 11b and the through
hole 21b.
[0047] As shown in FIGS. 1 and 8, the MEA 30, which serves as an
electrode structure, is configured such that predetermined catalyst
layers are formed on respective sides of an electrolyte membrane
EF; more specifically, an anode electrode layer AE is formed on the
side toward the gas flow space into which fuel gas is introduced,
and a cathode electrode layer CE is formed on the side toward the
gas flow space into which oxidizer gas is introduced. Since actions
(electrode reactions) of the electrolyte membrane EF, the anode
electrode layer AE, and the cathode electrode layer CE are widely
known and not directly related to the present invention, detailed
description thereof is omitted in the following description.
[0048] The electrolyte membrane EF is formed of an ion exchange
membrane (e.g., NAFION (registered trademark of a product of Du
Pont)) which is selectively permeable to cations (more
specifically, hydrogen ions (H.sup.+), or an ion exchange membrane
(e.g., NEOCEPTOR (registered trademark of a product of Tokuyama))
which is selectively permeable to anions (more specifically,
hydroxide ions (OH.sup.-). The size of the electrolyte membrane EF
is determined so as to be greater than a substantially square
opening which is formed when the resin sheet bodies 21 and 22 of
the frame 20 are superposed on each other, and so as not to cover
the through holes 21a and 21b and the through holes 22a and 22b
when the electrolyte membrane EF is sandwiched between the resin
sheet bodies 21 and 22. Such formation of the electrolyte membrane
EF prevents gas introduced into one gas flow space from leaking
into the other gas flow space (so-called crossleak).
[0049] The anode electrode layer AE and the cathode electrode layer
CE, which serve as the electrode layers in the present invention,
contain carbon (carrier carbon) which carries noble-metal catalyst
(e.g., platinum), or a hydrogen storage alloy, as a main component.
The anode electrode layer AE and the cathode electrode layer CE are
formed on the respective surfaces of the electrolyte membrane EF.
The anode electrode layer AE and the cathode electrode layer CE are
slightly smaller in size than the substantially square opening
which is formed when the resin sheet bodies 21 and 22 of the frame
20 are superposed on each other.
[0050] An exposed surface of each of the anode electrode layer AE
and the cathode electrode layer CE is covered with a carbon cloth
CC formed from electrically conductive fiber. The carbon cloth CC
is adapted to uniformly supply fuel gas or oxidizer gas supplied
into the corresponding gas flow space to an associated electrode
layer and to efficiently supply electricity generated through
electrode reactions to the associated collector 12. Since the
carbon cloth CC is fibrous, supplied gas flows through interfiber
space to thereby be uniformly diffused. Since the carbon cloth CC
is electrically conductive, the carbon cloth CC allows efficient
flow of generated electricity to the associated collector 12. The
carbon cloths CC may be eliminated as needed.
[0051] A single cell is formed by arranging in layers the separator
body 11, the collector 12, the frame 20, and the MEA 30.
Specifically, as shown in FIG. 7, the MEA 30 is disposed between
the two vertically arranged frames 20 which are disposed in such a
manner as to differ in an angular, planar orientation by about 90
degrees. The thus-arranged elements are joined together, for
example, through application of adhesive such that the electrolyte
membrane EF of the MEA 30 is sandwiched between the frames 20.
[0052] The collectors 12 are fitted into the resultant assembly of
the frames 20 and the MEA 30; more specifically, the collectors 12
are accommodated in the respective accommodation holes 21c and 22c
of the frames 20. At this time, the collectors 12 are accommodated
in the respective accommodation holes 21c and 22c of the frames 20
in such a manner that the opening direction of the through holes of
meshy arrangement of each of the collectors 12 (the metal laths MR)
coincides with the direction of arrangement of the paired through
holes 21a and 21b (through holes 22a and 22b) formed in the frame
20 in which the collector 12 is accommodated; i.e., the opening
direction coincides with the flow direction of introduced gas.
[0053] In a state where the collectors 12 are accommodated in the
respective accommodation holes 21c and 22c of the frame 20, the
separator bodies 11 are fixedly attached to the frame 20, for
example, through application of adhesive. Since the resin sheet
bodies 21 and 22 have a thickness slightly smaller than the formed
height of the collectors 12, attachment of the separator bodies 11
causes the collectors 12 to be slightly pressed against the MEA 30.
Thus, a good state of contact is established between the collectors
12 and the MEA 30 (more specifically, carbon cloths CC). A
plurality of the thus-formed cells are stacked in accordance with
required output, thereby yielding a fuel cell stack.
[0054] In the thus-configured fuel cell stack, as shown in FIG. 1,
among the stacked cells, the gas inlets 11a of the separator bodies
11 communicate with one another through the through holes 21a and
22a of the frames 20, and the gas outlets 11b of the separator
bodies 11 communicate with one another through the through holes
21b and 22b of the frames 20. Thus, hereinafter, a communication
passageway formed by the gas inlets 11a and the through holes 21a
and 22a of the frames 20 in each unit cell is called a gas supply
inner-manifold, and a communication passageway formed by the gas
outlets 11b and the through holes 21b and 22b of the frames 20 in
each unit cell is called a gas discharge inner-manifold.
[0055] When fuel gas or oxidizer gas is externally supplied through
the gas supply inner-manifold, the supplied fuel gas or oxidizer
gas is introduced into each of the gas flow spaces. The
thus-introduced fuel gas or oxidizer gas uniformly diffuses and
flows throughout the gas flow space by virtue of the collector
12.
[0056] Specifically, gas which is introduced into each of the gas
flow spaces from the gas supply inner-manifold flows toward the gas
discharge inner-manifold while contacting the collector 12 disposed
in the gas flow space. As mentioned previously, the collector 12 is
formed from the metal lath MR in which a large number of
substantially hexagonal through holes are formed in a meshy,
step-like arrangement. More specifically, a large number of through
holes of the collector 12 are in a staggered arrangement in
relation to a gas flow direction.
[0057] Thus, a flow of gas in the gas flow space becomes a
turbulent flow as a result of the gas passing through the through
holes formed in a staggered arrangement in the collector 12; i.e.,
in the metal lath MR. Thus, gas introduced from the gas supply
inner-manifold diffuses uniformly in the gas flow space; in other
words, a gas concentration gradient becomes uniform. By virtue of a
uniform gas concentration gradient in the gas flow space and
passage of gas through the carbon cloth CC, fuel gas and oxidizer
gas are supplied uniformly to the anode electrode layer AE and the
cathode electrode layer CE, respectively.
[0058] Furthermore, as mentioned previously, the collector 12 is
formed from the metal lath MR whose formed thickness is increased.
Thus, the collector 12 can ensure excellent gas diffusivity
mentioned above and can reduce flow resistance; i.e., pressure
loss, of gas flowing through the gas flow space. Additionally,
resistance associated with flow of gas introduced into the gas flow
space through a large number of uniformly formed small-diameter
through holes can also be reduced. Thus, gas can smoothly flow
through the gas flow space.
[0059] By virtue of uniform diffusion of gas and smooth flow of gas
through the gas flow space, the anode electrode layer AE and the
cathode electrode layer CE can efficiently perform electrode
reactions with supplied fuel gas and oxidizer gas, respectively. As
a result, the fuel cell can exhibit a greatly improved electrode
reaction efficiency. Also, since supplied gas can be effectively
utilized, unreacted gas reduces. Therefore, the fuel cell can
efficiently generate electricity.
[0060] Meanwhile, electricity that is generated efficiently by
virtue of improvement in electricity generation efficiency of the
fuel cell is output to the exterior of the fuel cell via the
collectors 12 and the separator bodies 11. In the collector 12, a
large number of small-diameter through holes are formed, and the
distance between the connection portions; i.e., the pitch P, is
small. Thus, the surface area per unit volume; i.e., the area of
contact with the MEA 30, is large. By virtue of the large area of
contact with the MEA 30, resistance associated with collection of
electricity generated in the MEA 30 (electricity collection
resistance) can be greatly reduced. Therefore, generated
electricity can be efficiently collected; i.e., electricity
collection efficiency can be improved.
[0061] In the MEA 30, which partially constitutes the polymer
electrolyte fuel cell, as well known, water is generated in the
anode electrode layer AE or the cathode electrode layer CE as a
result of electrode reactions using fuel gas and oxidizer gas.
Specifically, for example, in the case where the electrolyte
membrane EF of the MEA 30 is formed from an ion exchange membrane
selectively permeable to cations, water is generated in the cathode
electrode layer CE according to the following Reaction Formulas 1
and 2.
Anode electrode layer: H.sub.2.fwdarw.2H.sup.++2e.sup.- Reaction
Formula 1
Cathode electrode layer:
2H.sup.++2e.sup.-+(1/2)O.sub.2.fwdarw.H.sub.2O Reaction Formula
2
[0062] Also, for example, in the case where the electrolyte
membrane EF of the MEA 30 is formed from an ion exchange membrane
selectively permeable to anions, water is generated in the anode
electrode layer AE according to the following Reaction Formulas 3
and 4.
Anode electrode layer: H.sub.2+2OH.sup.-.fwdarw.2H.sub.2O+2e.sup.-
Reaction Formula 3
Cathode electrode layer:
(1/2)O.sub.2+H.sub.2O+2e.sup.-.fwdarw.2OH.sup.- Reaction Formula
4
[0063] When water is generated in large amount in the anode
electrode layer AE or the cathode electrode layer CE according to
the above formulas, supply of fuel gas or oxidizer gas may be
hindered; i.e., a flooding state may arise. Upon occurrence of the
flooding state, the generated water covers the surface of the anode
electrode layer AE or the cathode electrode layer CE and also
passes through the carbon cloth CC, thereby reaching the collector
12.
[0064] Meanwhile, the collector 12 is configured such that the
angle between the direction of formation of connection portions and
the direction of formation of through-hole formation portions for
forming the through holes is less than 90 degrees; in other words,
the pitch P is small, so that the through holes are in a steep
posture. Thus, for example, as compared with the case of formation
of the collector 12 from the metal lath SMR, the sequentially
formed through holes are arranged closer to one another with
respect to a gas flow direction. When the generated water reaches
the vicinity of the small-diameter through holes arranged close to
one another, by virtue of pressure of gas passing through the
through holes and the capillary action, the generated water which
has reached the collector 12 is well drained outward.
[0065] Specifically, in the collector 12 formed from the metal lath
MR, the pitch P is small; thus, a larger number of the planes of
openings of the formed through holes are in contact with the MEA 30
(more specifically, with the carbon cloth CC). Thus, the generated
water which has reached the collector 12 fluidly moves toward the
interiors of the through holes by the effect of capillary action
induced by its surface tension. In addition to the fluid movement
of the generated water, the pressure of gas flowing through the gas
flow space acts on the generated water. Thus, the generated water
which has reached the collector 12 is drained on the stream of a
portion of unreacted gas to the exterior of the fuel cell
stack.
[0066] As a result of the above-mentioned outward drainage of the
generated water which has reached the collector 12, for example,
excess water, which is the remainder of the generated water present
in the vicinity of the anode electrode layer AE or the cathode
electrode layer CE after consumption for moistening the electrolyte
membrane EF, reaches the vicinity of the collector 12 continuously
via the carbon cloth CC and is then drained. Such drainage of the
generated water is continuously performed during operation of the
fuel cell; in other words, so long as fuel gas and oxidizer gas are
supplied.
[0067] Thus, during operation of the fuel cell, by virtue of
capillary action in the collector 12 and flow of fuel gas or
oxidizer gas, the generated water is not stagnated in the collector
12. Also, excess generated water is not stagnated in the anode
electrode layer AE or the cathode electrode layer CE. Therefore,
the occurrence of a flooding state can be well prevented. Since,
during operation of the fuel cell, the generated water is
continuously drained to the exterior of the fuel cell stack, there
can be greatly reduced the amount of the generated water which,
after stopping of operation of the fuel cell, remains in the
individual cells; more specifically, in the anode electrode layers
AE or the cathode electrode layers CE, and in the collectors 12.
Thus, for example, even when the fuel cell is installed in an
environment susceptible to low temperatures (0.degree. C. or
below), a drop in supply of gas, which could otherwise result from
freezing of the generated water, can be prevented, so that the fuel
cell can exhibit good low-temperature start-up performance.
[0068] As will be understood from the above description, according
to the present embodiment, the collector 12 can be formed from the
metal lath MR in which a large number of small-diameter through
holes are formed in a meshy, step-like arrangement. Thus, fuel gas
or oxidizer gas separated by the separator body 11 can be well
diffused and supplied to the anode electrode layer AE or the
cathode electrode layer CE. The metal lath MR is manufactured in
such a manner that the angle between the direction of formation of
strand portions and the direction of formation of bond portions
becomes about 60 degrees. Thus, when the collector 12 is disposed
between the MEA 30 and the separator body 11, the plane of opening
of each of the through holes can have a large angle with respect to
the MEA 30 or the separator body 11 (i.e., the through holes can be
in a so-called steep posture).
[0069] Thus, for example, when the through holes of the metal lath
MR are rendered identical in diameter with the through holes of the
metal lath SMR, the thickness of the collector 12 can be increased.
In other words, even when the metal lath MR is formed with the same
working length and the same through-hole diameter as those of the
conventionally manufactured metal lath SMR, the collector 12 formed
from the metal lath MR can have an increased thickness. By virtue
of an increase in thickness of the collector 12, pressure loss
associated with flow of gas can be lowered, thereby ensuring
sufficient gas supply performance with respect to supply of fuel
gas and oxidizer gas required for electrode reactions in the MEA
30. Therefore, the electricity generation efficiency of the fuel
cell can be greatly improved.
[0070] By means of forming the collector 12 from the metal lath MR,
the distance between bond portions; i.e., the pitch P, in the
collector 12 can be reduced. In other words, the through holes of
the collector 12 can be arranged in proximity to one another. In a
state in which the through holes are in proximity to one another,
when water generated through electrode reactions reaches the
vicinity of the collector 12, the capillary action which arises in
the through holes renders the generated water more fluid. Also, in
a state in which fuel gas or oxidizer gas flows, in addition to the
capillary action, pressure for flow of gas acts on the generated
water. Thus, the generated water, together with a portion of
unreacted gas, can be efficiently drained to the exterior of the
fuel cell. Accordingly, even in a state in which water is generated
along with progress of electrode reactions, the generated water can
be well drained. Therefore, good gas supply performance can be
maintained through prevention of occurrence of flooding, whereby a
drop in electricity generation efficiency of the fuel cell can be
prevented.
[0071] Furthermore, since the pitch P in the collector 12 can be
reduced, contacts between the MEA 30 (more specifically, the anode
electrode layer AE or the cathode electrode layer CE, far more
specifically, the carbon cloth CC) or the separator body 11 and the
bond portions of the collector 12 can be rendered dense. Thus, the
collector 12 can efficiently collect and output electricity
generated through electrode reactions.
[0072] Also, particularly, the dense contacts between the MEA 30
and the collector 12 can greatly reduce deformation of the MEA 30,
whose substrate is a thin electrolyte membrane EF. Thus, a
mechanical load imposed on the MEA 30 can be greatly reduced,
thereby preventing deterioration of the MEA 30 which would
otherwise result from the imposition of mechanical load.
[0073] The present invention is not limited to the above-described
embodiment, but may be embodied in various other forms without
departing from the scope of the invention.
[0074] For example, in the above-described embodiment, the through
holes formed in the collector 12 (metal lath MR) have a
substantially hexagonal shape. However, no particular limitation is
imposed on the shape of the through holes formed in the collector
12 (metal lath MR) so long as fuel gas or oxidizer gas can pass
therethrough. For example, as shown in FIGS. 9(a) and 9(b), the
through holes can have a polygonal opening shape, such as a
quadrangular (diamond) opening shape or a pentagonal opening shape.
In this case, particularly, in the case of formation of through
holes having a quadrangular (diamond) opening shape, the upper
blade UH which serves as a shearing die may have a plurality of
substantially triangular cutting edges formed at predetermined
intervals.
[0075] According to the above-described embodiment, in formation of
a single cell, after the collector 12 is placed in each of the
accommodation holes 21c and 22c of the frame 20, the separator body
11 is assembled to each of the resin sheet bodies 21 and 22.
However, a single cell can also be formed as follows: after the
separator bodies 11 and the collectors 12 are respectively joined
together by a metal joining process, the collectors 12 are placed
in the respective accommodation holes 21c and 22c of the frame 20,
and the separator bodies 11 are assembled to the respective resin
sheet bodies 21 and 22. In this case, the separator body 11 and the
collector 12 may be joined together by a well-known process, such
as brazing, welding, or diffusion bonding.
* * * * *